Sealing means for spark plug electrodes



April 15, 1941. H. RABEZZANA arm.

SEALING MEANS FOR SPARK PLUG ELECTRODES Filed July 27, 1939 W. A {Hm I I u\\. 5 WW v zx 9 I 2 Patented Apr. 15, 1941 SEALING MEANS FOR, SPARK PLUG ELECTRODES Hector Rabezzana, Alexander J. Battey, and Lucian H. Wyatt, Flint, Mich., assignors to General Motors-Corporation, Detroit, Mich., a

corporation of Delaware Application July 27, 1939, Serial No. 286,824

1 Claim.

Our invention relates to spark plugs for use with internal combustion engines to ignite the combustible mixture supplied to and burned within the working cylinder thereof; and the object thereof is to provide more perfect sealing means associated with the insulated electrode of a spark plug for preventing leakage of gas along the electrode and through the passage provided for it in the porcelain or equivalent material insulating member of the plug. This, heretofore, has been a result diflicult to secure; and leakage of high pressure gases from the combustion chamber and along the central electrode has been a frequent cause of failure in spark plugs subjected to inordinately high temperature and pressure conditions, such as are present in modern internal combustion engines.

Our invention is illustrated in the drawing accompanying and forming a part of this specification, and wherein:

Figure l is a view showing a section of spark plug elements designed,'when completely assembled, to provide'a plug having sealing means in accordance with our invention.

Figure 2 is a view showing the upper end of the insulating member, with the central electrode in its final assembled position and sealed relative to the passage in the insulating member through which it extends.

Figure 3 is a view like Figure 2 except that no cement is present between the threaded part of the central electrode and the threaded passage in the insulating member with which said threaded part engages.

Referring now to the drawing, the numeral 5 designates the hollow metallic shell of a spark plug, and 5 the insulating member thereof made of porcelain or equivalent material. These parts, and features thereof shown' but not particularly described, are of ordinary and conventional form and, except as hereinafter appears, are not involved in the invention to which this present application relates.

The insulating member is provided with a passage extending longitudinally thereof and throughout its length, and through which the central and insulated electrode 1 of the plug extends; said passage being enlarged and interiorly threaded at its upper end as indicated by the numeral 8. The entrance to this threaded part 8 is beveled at an angle of about 45 degrees as indicated by the reference numeral 9 to receive the lower end of a sealing member III which provides a seal between the central electrode andthe insulating member.

The outer end of the electrode 1 is enlarged as shown and has an externally threaded portion II the thread of which engages the internally threaded passage 8, and has also a second threaded portion 12 whereby a current supplying lead may be connected to the central electrode. Between these threaded portions and formed either integrally with the central electrode, or separately therefrom and. secured thereto in any way so that the two form a unitary structure, is an annular flange I4 having a recess IS in its under side Within which the upper end of the sealing member l0 lies, as shown in Figures 2 and 3. This flange is preferably conical in form, as shown, so that the top wall of the recess I5 is inclined oppositely to the inclined wall 9; from which it follows that the sealing member ID will be both compressed and forced inward against the enlarged threaded upper end of the central electrode as the central electrode is screwed home from the position in which it is shown in Figure 1 into its final position shown in Figure 2.

The wall of the flange I4 is resilient, and the periphery thereof engages the upper end of the insulating member 6 when the parts are in the final position shown in Figures 2 and 3; from which it follows that the flange yields slightly as the electrode is screwed home, that the sealing member is subjected to a yielding pressure, and that such expansion as may occur due to change in temperature when the plug is in use is compensated for by the resilience of the flange and gastightness of the sealing means maintained irrespective of temperature variations.

The sealing member I0 is initially in the form of a ring i6 of rubber or similar plastic material, as shown in Figure 1, which ring is molded and shaped and made to assume a double conical form shown in Figure 2 as the .electrode is screwed into its final position shown in assembling the parts. The sealing member is thus subjected to a compressing action 8101.5 its axis and to a wedging action which forces it radially against the enlarged part I l of the electrode 1 thereby securing increased gastig'htness between the electrode and the insulating member of the plug.

Gastightness of the plug is due primarily to the sealing member l0 acting as above explained, and not to cement between the threaded portion ll of the electrode and the interiorly threaded part B of the passage through which the electrode extends. This idea is expressed in Fig= ure 3 which. shows our improved sealing means used without cement between the lower threaded end it and the interiorly threaded passage 8 into which the said end is screwed in assembling the parts. However and in order to secure better thermal conductivity between the central electrode and the insulating member, and to prevent the central electrode from unscrewing and perhaps becoming loose when the plug is in use, we commonly introduce a small quantity .of' cement of any suitable kind into the enlarged upper end of passage through which the central electrode extends (or coat the lower threaded part M with such a cement) whereupon and as the electrode is screwed into the position shown in Figure 2 the interstices between the threaded parts 8 and ill become filled with cement and the electrode will be restrained from unscrewing, and a better heat conducting path will be provided between the electrode and the insulating member. Such cement is indicated by numeral I]? in Figures 1 and 2.

Having thus described and explained our inaeeaeee vention we claim and desire to secure by Letters Patent:

in sealing means for the upper end of the insulated electrode of a spark plug and in combination with a spark plug insulator having a longitudinally extending passage the upper end of which is larger in diameter than the lower end thereof, and which enlarged upper end is interiorly threaded and the entrance to which interiorly threaded upper end is beveled; an electrode extending through said passage, and having an enlarged threaded portion engaging the interiorly threaded upper end of the passage aforesaid; an annular flange upon the enlarged upper end of said electrode, and which flange has a recess in its under side; and an annular deformable sealing member surrounding said elec trode and the upper end of which lies within said recess, and the lower end of which lies within the beveled entrance to said interiorly threaded passage.

HECTOR RABEZZANA.

AIEXANDER. J. BAT'IEY.

LUCIAN H. WYATT. 

